Optics
drorzel | January 18, 2011The latest snowstorm is wreaking some havoc on my plans for the day, which means I'm going to lift another question and answer from the Physics Stack Exchange, with some modification. This one is a question about thermal radiation:
What are the quantum mechanisms behind the emission and absorption of thermal radiation at and below room temperature? If the relevant quantum state transitions are molecular (stretching, flexing and spin changes) how come the thermal spectrum is continuous? What about substances (such as noble gases) which don't form molecules, how do they emit or absorb thermal…
drorzel | January 16, 2011I was at a meeting of the Committee on Informing the Public of the American Physical Society at the tail end of last week, so it seems appropriate to post a couple of APS-related announcements here on my return:
1) The APS has just created a Forum on Outreach and Engaging the Public. You may have read about this in the monthly APS News, but in case you missed it, there is a new organization with APS to bring people interested in outreach together:
"The forum provides a venue for people to congregate, provide best practice manuals...and disseminate things that work so people don't have to…
drorzel | December 28, 2010It's the last week of the (calendar) year, which means it's a good time to recap the previous twelve months worth of scientific news. Typically, publications like Physics World will publish a list of top ten physics stories of 2010, but we're all Web 2.0 these days, so it seems more appropriate to put this to a poll:
What is the top physics story of 2010?survey software
I've used the Physics World list as a starting point, because you have to start somewhere. I added a few options to cover the possibility that they left something out, and, of course, you know where the comments are.
This poll…
drorzel | December 15, 2010I've mentioned before that I'm answering the occasional question over at the Physics Stack Exchange site, a crowd-sourced physics Q&A. When I'm particularly pleased with a question and answer, I'll be promoting them over here like, well, now. Yesterday, somebody posted this question:
Consider a single photon (λ=532 nm) traveling through a plate of perfect glass with a refractive index n=1.5. We know that it does not change its direction or other characteristics in any particular way and propagating 1 cm through such glass is equivalent to 1.5 cm of vacuum. Apparently, the photon…
drorzel | December 1, 2010I hadn't heard anything about Dance of the Photons: From Einstein to Quantum Teleportation before it turned up in my mailbox, courtesy of some kind publicist at Farrar, Straus, and Giroux, otherwise I would've been eagerly anticipating it. Anton Zeilinger is a name to conjure with in quantum optics, having built an impressive career out of doing laboratory demonstrations of weird quantum phenomena. He shared the Wolf Prize earlier this year with John Clauser and Alain Aspect, and the three of them are in a small set of people who probably ought to get a Nobel at some point in the near future…
drorzel | November 19, 2010Earlier this week, I talked about the technical requirements for taking a picture of an interference pattern from two independent lasers, and mentioned in passing that a 1967 experiment by Pfleegor and Mandel had already shown the interference effect. Their experiment was clever enough to deserve the ResearchBlogging Q&A treatment, though, so here we go:
OK, so why is this really old experiment worth talking about? What did they do? They demonstrated interference between two completely independent lasers, showing that when they overlapped the beams, the overlap region contained a pattern…
drorzel | November 15, 2010This is adapted from an answer to a question at the Physics Stack Exchange site. The questioner asked:
It seems that if the coherence length of a laser is big enough, it is possible to observe a (moving) interference picture by combining them. Is it true? How fast should photo-detectors be for observing of the interference of beams from two of the "best available" lasers?
This is a question about the itnerference of light waves, which is traditionally demonstrated via the famous "double slit" experiment, where a single laser is sent through a barrier with two narrow slits cut in it. The…
drorzel | September 3, 2010Over at Confused at a Higher Level, Melissa offers an alphabetical list of essential supplies for a condensed matter experimentalist at a small college. This is a fun idea for back-to-school time, so I'll steal it, and offer the following alphabetical list of essentials for Atomic, Molecular, and Optical physics at a small college, kind of a condensed version of the three part series I did a few weeks ago.
A is for Acousto-optic modulator This is a device that uses sound waves in a crystal to deflect light and shift its frequency. It's essential for rapid control of laser properties.
B is for…
drorzel | August 30, 2010Last week, John Baez posted a report on a seminar by Dzimitry Matsukevich on ion trap quantum information issues. In the middle of this, he writes:
Once our molecular ions are cold, how can we get them into specific desired states? Use a mode locked pulsed laser to drive stimulated Raman transitions.
Huh? As far as I can tell, this means "blast our molecular ion with an extremely brief pulse of light: it can then absorb a photon and emit a photon of a different energy, while itself jumping to a state of higher or lower energy."
I saw this, and said "Hey, that's a good topic for a blog post…
drorzel | August 24, 2010Two papers in one post this time out. One of these was brought to my attention by Joerg Heber, the other I was reminded of when checking some information for last week's mathematical post on photons. They fit extremely well together though, and both relate to the photon correlation stuff I was talking about last week.
OK, what's the deal with these? These are two papers, one recent Optics Express paper from a week or so ago, the other a Nature article from a few years back. The Nature paper includes the graph you see at right, which is a really nice dataset demonstrating the Hanbury Brown and…
drorzel | August 20, 2010In my post about how we know photons exist, I make reference to the famous Kimble, Dagenais, and Mandel experiment showing "anti-bunching" of photons emitted from an excited atom. They observed that the probability of recording a second detector "click" a very short time after the first was small. This is conclusive evidence that photons are real, and that light has discrete particle-like character. Or, as I said in that post:
This anti-bunching effect is something that cannot be explained using a classical picture of light as a wave. Using a wave model, in which light is emitted as a…
drorzel | August 18, 2010Most of the time, when we talk about seeing quantum effects from light, we talk about extremely weak beams-- looking at intensities where one photon more or less represents a significant change in the intensity of the light. Last week, though, Physics Buzz wrote up a paper that goes in the other direction: they suggest a limit on the maximum strength of a laser pulse due to quantum effects, specifically the creation of particle-antiparticle pairs.
This is a little unusual, in that most of the time when people talk about really intense lasers, they end up discussing them as an oscillating…
drorzel | August 13, 2010Some folks I used to work with at NIST have looked at cheap green laser pointers, and found a potential danger. Some of the dimmer-looking green lasers are not so dim in the infrared, and in one case emitted 10X the rated power in invisible light. This could be a potential eye hazard.
You can read their full report on the arxiv. It's got a nice description of how green laser pointers turn infrared light into visible light, which is really pretty awesome-- a guy I met at a conference once declared them the coolest invention ever, because it's "quantum optics in the palm of your hand." Better…
drorzel | August 12, 2010Following on yesterday's discussion of the vacuum hardware needed for cooling atoms, let's talk about the other main component of the apparatus: the optical system. The primary technique used for making cold atoms is laser cooling, and I'm sure it will come as no surprise that this requires lasers, and where there are lasers, there must also be optics.
There are lots of different types of lasers used for laser cooling experiments, but they all need to have certain properties: tunability, stability, and adequate power. Tunability is important because laser cooling requires light at exactly…
drorzel | July 23, 2010This week's big story in physics is this Science paper by a group out of Austria Canada (edited to fix my misreading of the author affiliations), on a triple-slit interference effect. This has drawn both the usual news stories and also some complaining about badly-worded news stories. So, what's the deal?
What did they do in this paper? The paper reports on an experiment in which they looked at the interference of light sent through a set of three small slits, and verified that the resulting pattern agrees with the predictions of the Born rule for quantum probabilities.
What does Matt Damon…
drorzel | June 28, 2010Last week, Dmitry Budker's group at Berkeley published a paper in Physical Review Letters (also free on the arxiv) with the somewhat drab title "Spectroscopic Test of Bose-Einsten Statistics for Photons." Honestly, I probably wouldn't've noticed it, even though this is the sort of precision AMO test of physics that I love, had it not been for the awesome press release Berkeley put together, and this image in particular (grabbed with its caption):
This is a nifty paper, and deserves a little explanation in Q&A format:
Is this another New Scientist style "Einstein was wrong" paper? No. If…
drorzel | June 22, 2010A press release from Harvard caught my eye last week, announcing results from Markus Greiner's group that were, according to the release, published in Science. The press release seems to have gotten the date wrong, though-- the article didn't appear in Science last week. It is, however, available on the arxiv, so you get the ResearchBlogging for the free version a few days before you can pay an exorbitant amount to read it in the journal.
The title of the paper is "Probing the Superfluid to Mott Insulator Transition at the Single Atom Level," which is kind of a lot of jargon. The key image is…
drorzel | June 5, 2010Over at Tor.com, Kate has a Lord of the Rings re-read post about the Battle of the Pelennor Fields, which includes a shout-out to me that I missed because I was driving to NYC:
Ãomer is "scarely a mile" away when the standard unfurls and is clearly seen to bear the White Tree, Seven Stars, and a high crown. If I were at home, I could ask the resident scientist to tell me how big these elements would need to be to be visible at a mile, but I'm finishing this post on the train down to New York City (vacation! Woo! I'm going to try and write the next post while I'm there, too, so as to make up…
drorzel | June 2, 2010I mentioned in a previous post that one of the cool talks I saw at DAMOP had to do with generation of coherent X-Ray beams using ultra-fast lasers. What's particualrly cool about this work is that it doesn't require gigantic accelerators or nuclear explosions to produce a laser-like beam of x-rays-- it's all done with lasers that fit on a normal-size optical table in an ordinary lab room.
The specific talk I saw was by Margaret Murnane of JILA, who co-leads their ultra-fast laser group, and dealt with a new technique for producing soft-x-rays (~500 eV photons) with ultrafast lasers. We'll do…
drorzel | June 1, 2010While I mostly restricted myself to watching invited talks at DAMOP last week, I did check out a few ten-minute talks, one of which ended up being just about the coolest thing I saw at the meeting. Specifically, the Friday afternoon talk on observing relativity with atomic clocks by Chin-Wen Chou of the Time and Frequency Division at NIST in Boulder.
The real technical advance is in a recent paper in Physical Review Letters (available for free via the Time and Frequency Publications Database, because government research isn't subject to copyright): they have made improvements to their atomic…